The use of synthetic fluorogenic substrate has been applied to the measurement of lipase from guinea pig epidermis. The enzyme is not inhibited by Triton X-100 in concentrations up to 2 mg/ml, has a pH optimum in the range 6.5–8.5, a Km of 1.0 × 10––6 mol/l for 4-methyl umbelliferyl butyrate and possesses maximum activity towards esters of chain length C5–C6. The levels of activity observed seem sufficiently high to preclude bacterial flora as the major source. It is therefore concluded that skin possesses endogenous lipase